EINVAL An invalid value was passed in flags or event_f_flags.
FAN_ALL_INIT_FLAGS (deprecated since Linux kernel version
4.20) defines all allowable bits for flags.
EMFILE The number of fanotify groups for this user exceeds 128.
EMFILE The per-process limit on the number of open file
descriptors has been reached.
ENOMEM The allocation of memory for the notification group
failed.
ENOSYS This kernel does not implement fanotify_init(). The
fanotify API is available only if the kernel was
configured with CONFIG_FANOTIFY.
EPERM The operation is not permitted because the caller lacks
the CAP_SYS_ADMIN capability.
